Over the past year, we have used in situ hybridization method to assess the relative expression of candidate genes selected by SAGE and cDNA array analysis. We used fresh frozen tissue sections from lung cancers with surrounding normal and hybridize the tissue with biotin labeled probes of candidate genes. The hybridization signal is then visuallized using a tyramide based method. We have thus far surveyed nearly 50 fresh frozen lung tumor samples and 21 of those were suitable for in situ hybridization. Using these tissues, we have screened five genes for their differential expression in lung cancers and identified a potential tumor marker that is expecifically expressed in 90% of the tumors examed but not present in the normal lung. We are currently determining the relative expression of this candidate marker in a large panel of paraffin embedded lung tissues to determine the clinical significance of this gene's expression in lung cancer. We are also screening additional genes that are differentially expressed in lung cancer.